The 06 GT has 300hp (as will the 07 and the 08 and probably the 09).
In 07 you can buy the 500hp Shelby GT500.
In 08 they'll add a Boss (probably with 5.4 na at 400hp, and probably called a SVT product), with a Bullit variant to celebrate the 40th anniversary of the movie.
In 09 they'll finally add the Mach 1 (dohc at about 375hp) to round out the line, just in time for the major redesign in 2010 (if this scenario sounds like what they did 99-2004, you're right, except now we don't have the maverick SVT group making things as interesting anymore - hence no SVT Cobra - though some will be confused by the use of SVT badges on the Shelby).
Look for Dodge to hammer Ford with their Hemis, including several coupe designs (2007 Challenger derived from the Charger is a good bet, and they'll have a Chrysler version as well - probably 2008 replacement for the Crossfire being phased out in 2009).
Look for GM to finally get the GTO off the dime (new styling this year is down payment on this), and come up with variant off of another platform-yet-to-be-named for the new Camaro and Firebird pony cars (marketing space is tight, but they really don't have much choice here) in 2008. This is a year behind where they should be, but that's the current GM for you - years late and billions of dollars short.
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RE: stang getting more power - 
